1. Field of the Invention
The present invention relates to a transmission method, a transmission system, a transmission device and a reception device for sending a modulated digital signal from the transmission device to the reception device.
2. Description of Related Art
A plurality of wireless communication systems, e.g. a mobile phone, wireless Local Area Network (LAN), broadband wireless LAN such as Worldwide Interoperability for Microwave Access (WiMAX) and the like, have been in practical use. Increase of such wireless communication systems has caused a problem of shortage in available frequency resources. The problem is worse especially in a band of 6 GHz or lower which is densely used by mobile phones or the like. To solve the problem, researches concerning cognitive radio have been carried out.
The cognitive radio is a technical proposal for highly sharing a frequency among a plurality of wireless systems so as to aim for upgrading of wireless communication systems. The cognitive radio allows a wireless device such as a terminal, a base station or the like to have a functional capability of recognizing or cognizing surrounding radio wave environment. It is for a wireless device to select a frequency, a scheme and the like used in wireless communication for itself in accordance with the recognized or cognized radio wave environment to enhance the use efficiency of a frequency. This enables the user to receive the benefit of high speed data communication and stable communication services.
Moreover, in a transmission scheme for uplink in 3rd Generation Partnership Project (3GPP), Single Carrier transmission Frequency Division Multiple Access (SC-FDMA) has been considered as a technology for realizing effective use of a spectrum in an assigned band. For SC-FDMA, a technology of suitably inserting a 0 spectrum between spectra after Discrete Fourier Transform (DFT) has been proposed (see Non-Patent Document 1 for example).